Title: Chromium, Insulin and Glucose
Key words: chromium, LMWBS, insulin, glucose tolerance factor
Date: April 2000
Category: 3. Micronutrients
Author: Dr van Rhijn
Chromium, Insulin and Glucose
Low Molecular Weight Chromium Binding Substance
Low molecular weight chromium binding substance (LMWCr)1 is a naturally occurring, Cr-binding polypeptide. It was first identified in bovine colostrums and isolated from a variety of mammals but no human equivalent has yet been identified. LMWCr does not affect the binding of insulin, but has a physiological post-receptor role inside insulin-dependent cells, displaying a biological activity similar to GFT. It can be isolated and characterised at a molecular level using spectroscopic and magnetic techniques2. LMWCr provide an essential biologically active form of Cr (III), potentiating the effect of insulin for carbohydrate and lipid metabolism by activating (directly proportional to the amount of LMWCr) insulin receptor tyrosine kinase 3 and phosphotyrosine phosphatase (PTP) activity in membranes 4.
1 Yamamoto, A. et al.. Purification and properties of biologically active chromium complex from bovine colostrum. J. Nutr. 1988; 118: 39 - 45.
2. Vincent, J.B.. Low-Molecular-Weight Chromium-Binding-Substance and synthetic models. J. Inorg. Biochem. 1993; 51: 77.
3. Vincent, J.B.. Mechanisms of chromium action: low-molecular-weight chromium-binding substance. J. Am. Coll. Nutr. 1999; 18:1, 6 - 12.
4. Davies, C.M. et al.. A biologically active form of chromium may activate a membrane phosphotyrosine phosphatase (PTP). Biochem. 1996; 1; 35(39): 12963 - 12969.
Schwartz & Mertz coined the term, ‘glucose tolerance factor’1 (GFT) to describe a compound extracted from porcine kidney that restored impaired glucose tolerance in rats. Chromium (Cr) was identified as the essential element2 potentiating insulin action3. The factor extracted from brewers’ yeast4, contained chromium, nicotinic acid, glutamic acid, glycine and the sulphur-containing amino acid cysteine. The exact structure of the active compound remains uncertain (difficulty in purifying or synthesizing)5. Controversy regarding its role exists, some researchers suggest it is a nutrient6, supplying Cr to Cr-deficient species to improve glucose metabolism, thereby lowering the affinity of insulin for its receptor by binding GFT, rendering insulin unrecognisable by the receptor7. Mertz8 disagree that GTF bind insulin and provides evidence that insulin acts in the presence of GFT9, suggesting that Cr influences glucose metabolism via its effects on cell transport10. Other studies suggest the Cr action mechanism involves increased insulin binding with subsequent increased insulin receptor numbers and receptor phosphorilation11. Various trivalent Cr supplementation studies confirmed the intracellular role of Cr in diabetes by improving glycaemic control12,13, and insulin resistance.